1. Technical Field
The present disclosure relates to PWM (Pulse width modulation) control systems, and more particularly to a PWM control system with both single-phase and multi-phase PWM signals.
2. Description of Related Art
Referring to FIG. 1, an example of a 4-phase power supply for a CPU (Central Processing Unit) of a motherboard includes a 4-phase PWM controller sending a PWM signal. The PWM signal includes four phase outputs connecting to four driver ICs (Integrated Circuit) correspondingly. Each of the driver ICs is adapted to switch on/off a pair of MOSFETs for adjusting an output voltage (Vout) supplied to the CPU. Relative to a single-phase power supply, a multi-phase power supply utilizes many pairs of MOSFETs, thereby capable of decreasing a working time of each of the MOSFETs and decreasing heat generated by each of the MOSFETs. Thus, components of the multi-phase power supply performance more reliably.
A typical PWM control system for adjusting the CPU power supply may utilize both a multi-phase PWM controller and single-phase PWM controllers. The multi-phase PWM controller and the single-phase PWM controllers can operate individually or jointly for ensuring the CPU power supply is continuous and at an appropriate voltage level.
FIG. 2 illustrates waveforms of PWM signals and associated ripple currents in the typical PWM control system. PWM1 signal is a 4-phase signal (Phase1, Phase2, Phase3, and Phase4). PWM2 signal and PWM3 signal are both single-phase signals. Pulses of the PWM2 signal is delayed relative to that of the Phase1 signal of the PWM1 signal, and pulses of the PWM3 signal is delayed relative to that of the phase2 signal of the PWM1 signal. A delay time T is ½ cycle (180 degrees). Only one pulse of the PWM2 or PWM3 signal can be inserted in one cycle [f1] of the PWM1 signal. Then, the pulses of the PWM1, PWM2, PWM3 signals are regular, and ripple currents associated with the PWM1, PWM2, PWM3 signals are not superposed, and a total ripple current is not increased. However, a pulse frequency of the PWM signals (PWM1, PWM2, and PWM3) cannot be further increased since only one pulse of the PWM2 or PWM3 signal can be inserted in one cycle of the PWM1 signal.